1. Field of the Invention
The present invention generally relates to wavelength division multiplexing systems (WDM systems), and more particularly an optical supervisory transmission signal control device necessary for network management when an optical transmission takes place between a transmission-side terminal device and a reception-side terminal device via an optical amplifier/repeater device.
2. Description of the Related Art
Recent data transmission has been required to transfer data at an extremely high speed over a long distance. In addition, such data transmission has been required to be implemented by a low-cost system such as a WDM system.
The WDM system generally includes a transmission-side terminal device, an optical amplifier/repeater device, and a reception-side terminal device. The terminal device on the transmission side wavelength-multiplexes a plurality of signal lights having mutually different wavelengths and sends a multiplexed optical signal to an optical fiber. The optical amplifier/repeater device is placed in the way of the optical fiber transmission path in order to realize long-distance transmission. The terminal device on the reception side receives the multiplexed optical signal from the transmission path and wavelength-demultiplexes the received optical signal.
In the WDM system, an optical supervisory channel frame having a wavelength different from the wavelengths of the signal lights is transferred between the devices in order to control the gains of optical amplifiers of the devices. Hereinafter, the optical supervisory channel frame will be abbreviated as OSC frame. The OSC frame is used to inform the optical amplifiers of the devices of supervisory control information concerning respective input signals applied to the optical amplifiers. Hence, the gains of the optical amplifiers are controlled.
In the WDM system, an in-service migration is taken into account in the terminal device on the transmission side when or after the WDM system is built up. The in-service migration means that channels to be wavelength-multiplexed are added or channels are altered to accommodate signals having different bit rates. In this case, it is important to perform, from the remote side, setting of provisioning for gain control of the optical amplifier in the optical amplifier/repeater device or the reception-side terminal.
In ordinary optical transmission systems that do not perform wavelength multiplexing, the role of the above-mentioned OSC frame is played by data placed in an overhead (OH). The OSC frame has a different specification and format from the OH data. Hence, the OSC frame cannot be handled in conventional supervisory control blocks which handle the OH data. Thus, the conventional WDM system be required to develop a particular supervisory control block capable of controlling the OSC frame.
In practice, it is very advantageous, even in terms of cost, to develop functions commonly used for various applications that are required to build networks. In this regard, it is required that the supervisory control block which handles the OSC frame is unified with the block that handles the OH data and can thus handle the OH data.
For example, a network shown in FIG. 1 will be considered. In the network, nodes use both the WDM system using the OSC frame as the supervisory control information and the ordinary optical transmission system using the OH data as the supervisory control information. In this case, the supervisory control blocks of the nodes are required to be capable of processing both the OSC frame and the OH data. In this case, merely adding software directed to realizing the function of processing data contained in the OSC frame to the supervisory control block capable of handling the OH data may be considered. However, this will increase the load on CPUs of the supervisory control blocks, and software executed by the CPU will be restricted.
In the conventional WDM system, DCC, order wire, and multiplexed wavelength information are processed in the supervisory control blocks. The DCC and the order wire employ an interface synchronized with a clock. Hence, the supervisory control blocks have a large number of wires for electrical connections. In practice, the interface is formed by a number of boards that are arranged in a stacked formation.
It is a general object of the present invention to provide an optical supervisory transmission signal (frame) control device in which the above disadvantages are eliminated.
A more specific object of the present invention is to provide an optical supervisory transmission signal control device which can use a wavelength-multiplexed optical transmission system and another optical transmission system without increasing software executed in a processor provided in a supervisory control block.
The above objects of the present invention are achieved by a control device for processing an optical supervisory transmission signal necessary for network management between transmission devices in a wavelength-multiplexed optical transmission system, the above control device comprising: a main signal device that amplifies a main signal light which is wavelength-multiplexed; a supervisory control device that processes supervisory control information; and a transmission path connecting the main signal device and the supervisory control device. The supervisory control information is defined by mapping items of data of the optical supervisory transmission signal into an overhead defined in another optical transmission system. The main signal device converts the optical supervisory transmission signal dropped from the main signal light into the supervisory control information, which is sent to the supervisory control device. The supervisory control device processes the supervisory control information received as the overhead.
The control device may be configured so that the main signal device converts the supervisory control information received from the supervisory control device into the optical supervisory transmission signal, which is added to the main signal light.
The control device may be configured so that the main signal device comprises: a generation/termination part which performs a conversion between the supervisory control information and the optical supervisory transmission signal; and a transmission part which transfers the supervisory control information between the main signal device and the supervisory control device, wherein an interface between the generation/termination part and the transmission part includes a start-stop synchronization in which a start bit, a parity bit and a stop bit are added to the supervisory control information.
The control device may be configured so that the transmission path is an ATM transmission path over which an ATM cell is transferred between the main signal device and the supervisory control device.
The control device may be configured so that the main signal device receives an ATM cell in which the supervisory control information is arranged from the supervisory control device, and sends the supervisory control information arranged in the received ATM cell to a generation/termination part of the main signal device, which supervisory control information corresponds to information arranged in a header of the received ATM cell.
The control device may be configured so that the main signal device comprises: a first part that receives an ATM cell in which the supervisory control information is arranged from the supervisory control device; a second part that determines whether a fault has occurred in the transmission path by referring to a fault detection signal related to the transmission path and included in the ATM cell; and a third part that fixes, if occurrence of a fault is detected, the supervisory control information to be sent to a generation/termination part of the main signal device to that obtained before the fault occurred.
The control device may be configured so that the main signal device comprises: a first part that receives an ATM cell in which the supervisory control information is arranged from the supervisory control device; a second part that determines whether a fault has occurred in the transmission path by referring to error check data included in the ATM cell; and a third part that maps, if an error is detected, error information in an ATM cell, which is sent to the supervisory control device.